Photographic detection of slowly moving neutrons



Patented Jan. 9, 1940 PATENT OFFICE PHOTOGRAPHIC DETECTION OF SLOWLY MOVING NEUTRONS Hartmut Kallmann, Berlin-Charlottenburg, and

Ernst Kuhn, Berlin, Germany, assignors to I. G. Fa'-benindustrie Aktiengesellschaft, Ludwigshafen-on-tle-Rhine, Germany, a co'poratlon of Germany Application March 24, 1938. Serial No. 197329 In Germany March 25, 1937 13 Claims. (CI. 250-83) This invention relates to a method for the detection of slowly moving neutrons, and has for its principal object the provison of a method by which slowly moving neutrons may be detected photographically.

Slowly moving neutrons -are only slightly. absorbed by lead, but are strongly absorbed by wateror hydrogen-containing substances, such 'as Wood or the like. They behave, in this respect,

exactly opposite to X-rays. If, therefore, a body composed of difierent substances is transilluminated by a beam of slowly moving neutrons the intensity distribution of the neutron beam leaving the body is difierent from the intensity distribution in an X-ray beam after it has penetrated the same body. If the beam of slowly moving neutrons could be made visible by means of a lumnous screen or a photosensitive material a difierent image would be obtained in the transillumi'nation with slowly moving neutronsthan with X-rays. The investigation of substances by means of slowly moving neutrons would be' important, therefore, not only for medical purposes but also for technical investigations. It would be possible, for example, to investigate materials contained in metallic receptacles if the materials were such as to absorb the neutrons more strongly than they are absorbed by the metallic walls of the vessel, for example, if the materials comprise hydrogen-containing subtances.

i slowly moving neutrons are almost entirely unable to affect photosensitive coatings. If slow neutrons are to be detected, therefore, an intermediate reaction must be introduced which results in the production of particles capable of `blackening the photographic plate.

The invention 'comprises the photographic detection of slowly moving neutrons by utilizing an interposed reaction that results in the produc- 40 `tion of heavily charged particles which have a greatly increased efiect on photosensitive coatings. This is' accomplished by using plates or films including a lithium foil. The slowly moving neutrons react with the nuclei of lithium in such a way that heavy charged particles suchas Ha or He' are produced. In order that the lithium will not attack the photographic coating, it is desirable to interpose an intermediate layer between it and the coating. The intermediate layer should, however, be very easily penetrable by the Ha or He particles produced in the intermediate reaction, for example, a thin aluminium foil may be used; or plates or films can be used on which already been applied.

The invention is illustrated by the accompanying drawing in which:

Fig. l is a diagrammatic section of an illustrative embodiment of the inventiom and Figs. 2, 3 and 4 are diagrammatic sections of 8 modified-embodiments of the inventio'n. g

In the drawing, l is a support, 2 is a layer of photosensitive material, for example, silver halide gelatine emulsioh, 3 is a protective layer comprising a thin aluminum foil, and 4 is a layer of 10 lithium foil.

The thickness of the aluminum foil may be' about 0.0005 mm., the thickness of the layer of lithium may be about 0.1 mm.

For increasing the ei'fect, it is advisable to use 15 double-coated films or plates, as shown in Figure 2, or to place a plurality of films or plates one behind the other, as shown in Fig. 3, lithium' foil with a protective coating being associated with each of the sensitive coatings. Since the lithium zo foil oxldizes easily in air and thereby becomes less efi'ective, it is advisable to enclose it in an airtight manner. Airtight receptacles that are either exhausted, as shown in Flgure 4, or filled a with an inert gas are preferably used for this 25 purpose.

Insteadof the lithium foil, layers of a lithium compound may be used. The eflect of such compounds is less, however, since in the effective a layer of photosensitive material. covered with lithium foil. 40

3. A device for for'ming a photographic image of a beam of slowly moving neutrons comprising a layer of photosensitive material covered with lithium foil and having interposed between the lithium foil and the photosensitive material a 45 protective layer.

4'. A device for forming a photographic image of a beem of slowly moving neutrons comprising a layer of photosensitive material covered with lithium foil and having interposed between the 0 lithium foil and the -photosensitive material a thin aluminium foil passable by the particles produced by the interaction of the slowly moving neutrons with the lithium atoms.

5. A device for forming a photographic image u foil.

of a beam of slowiy moving neutrons comprieing a layer of photosensitivematerial aseociated with a layer containing lithium atoms, a gastight receptacle surrounding said layers, the interier of said receptacle being substantially free from air.

6. A device for forming a photographic image of a beam of slowly moving neutrons comprising a layer of photosensitive material associateol With a layer containing lithium atoms, a gastight receptacle surrounding said iayers, the interior of said receptacle being evacuated.

7. A device for forming a photographic image of a beam of slowly moving neutrons comprising a layer of photosensitive material associated with a layer containing lithium atoms a gastight receptacle surrounding said layers, the interier oi said receptacle being filled with an inert gas.

8. A tlevice for forming a photographic image 9. A device for forming a. photographic image of a beam of slowly moving neutrons comprising a plurality of supporting layers, a. layer of photosensitive material on each sur'ace of said supporting layers, lithium foil associated with each layer of photosensitive material and'a protective layer between each photosensitive layer and the lithium ioil. I

10. A method of forming a photographic image by means of slowly moving neutrons which comprises applying a layer of a substance containing iithium atoms to a layer ofphotosensitive ma.- terial and exposing the associated layers to the action of a beam of slowly moving neutrons.

11. A method ot forming a photographic image by means of slowly moving neutrons which comp-ises applying a lithium foil to a layer of photosensitive material and exposing the associated layers to the action oi' a bean of slowly moving neutrons.

12. A method of forming a photographic image by means oi slowly moving neutrons which comprises applying a protective layer to a layer of photosensitive material, applying a layer of lithium foil upon said protective layer, and exposing the associated layers to the action of a beam of slowly moving neutrons.

13. A method of forming a photographic image by means of slowly moving neutrons which comprises applying a thin aluminum !oil to a layer of photosensitive material, applying a layer of lithium ioil upon said aluminum foil, and exposing the associated layers to the action of a beam of slowly moving neutrons.

HARTMUT KAILMANN. 4 ERNST KUHN. 

